Miniature electrical switch



March 4, 1969 w. a. AMBLER ET AL MINIATURE ELECTRICAL SWITCH Filed Jan. 5, 1967 E R m T N 9 I T E Y R A w E E A M M A 6. B M R z E m B L \\\\\\\\\\\k\\\\- .7 1 O A 1/6 A ww R W fll I. v V. I i t n N.% B O I w QM N\ VV M T b. QQRWSIQ .x w q n nw xi ww United States Patent 3,431,526 MINIATURE ELECTRICAL SWITCH Walter B. Ambler, Norwood, and Robert G. Mawney,

Attleboro, Mass, assignors to Texas Instruments Incorporated, Dallas, Tern, a corporation of Delaware Filed Jan. 3, 1967, Ser. No. 606,672 US. Cl. 337-89 11 Claims Int. Cl. H01h 61/02 ABSTRACT OF THE DISCLOSURE A miniature hermetically sealed thermally responsive electrical switch especially useful for placing directly on the windings of a fractional horsepower motor to serve as a protector therefor. The hermetic seal of the switch is protected from deleterious effects of arcs created on the making and breaking of the switch contacts by positioning the contacts relatively remotely from the seal and arranging the component parts such that the current path causes the arc to be blown away from the sealed end of the switch. A heater is provided which provides anticipatory heat and acts as a heat sink to extend the off (contacts-open) time of the switch. A simple header is provided having a sharp peripheral edge which acts as the weld projection for welding to a cooperating flared can. A stop member is provided in one embodiment to limit the travel of the thermally responsive snap acting disc and to adjust the contacts gap. The can is provided with a flattened area to facilitate attachment to the motor windings. Various terminal connectors are disclosed including a swaged terminal connector.

Background of the invention This invention relates to thermally responsive electrical switches and more particularly to such switches which are useful as protectors for electric motors. There has been a need for an improved protector which is both current and temperature sensitive and is especially useful for fractional horsepower motors employed in refrigerators and air conditioners. It is known to use external protectors but these have the problem of not following the winding temperature closely enough. Further, when used in refrigerator and air conditioner applications, such prior art devices will not protect the motor from. harm occasioned by a loss of the cooling medium employed, e.g., Freon. The switch of the present invention may be placed within the fluid medium since it employs a hermatic seal to prevent entrance of the fluid contiguous thereto. It is also useful for motors located in hazardous surroundings such as sub-merged pumps in gasoline tanks. The instant invention offers a device which although miniature in size is conducive to mass production manufacturing techniques. Further, due to the unique construction the seal is protected from deleterious effects of arcs which occur between the contacts on making and breaking thereof and an extended off time. t

It is an object therefore to provide an overload protective switch which will effectively protect fractional horsepower electric motors against various types of overload condition including both locked rotor and running overload types such as in the case of a refrigerator or air conditioner by a loss of cooling medium. It is a further object to provide such a switch which is reliable in operation, has a minimum number of components and is relatively simple to enhance assembly thereof.

The invention accordingly comprises the elements and combination of elements, features of construction, and arrangements of parts which will be exemplified in the structure hereinafter described, and the scope of the ap- Patented Mar. 4, 1969 plication of which will be indicated in the appended claims.

' Brief description of the drawings In the accompanying drawings in which several of the various possible embodiments of the invention are illustrated:

FIGURE 1 is a top plan view in cross section of an electrical switch according to one embodiment of the present invention;

FIGURE 2 is an elevational, cross sectional view of the switch taken on line 2--2 of FIGURE 1;

FIGURE 3 is a cross sectional view' of the switch taken on line 33 of FIGURE 2;

FIGURE 4 is an elevational view of a second embodiment with the housing removed; and

FIGURE 5 is a partial view of a modification of the terminal pin structure.

Dimensions of certain of the parts as shown in the drawings may have been modified for purposes of clarity of illustration.

Descriptio of preferred embodiment FIGURES 1-3 show a. heat and current sensitive thermally responsive switching device according to one embodiment generally referred to by numeral 10.

Switch 10 comprises a metallic electrically and thermally conductive housing or can 12 having a closed end 14 and an open flared end, 16.

The internal thermally responsive assembly of switch 10 is mounted on a header member 18 formed of conventional electrically conductive material and is generally annular in shape. A terminal pin 22 extends through bore 20 in header 18 and is mounted and electrically isolated from the header by a glass seal of either a compression or a matched type, well known in the art. The inside peripheral edge 26 of header 118 forms a relatively sharp corner or edge and cooperates with flared portion 16 of ca 12 by serving as a weld projection for hermetic attachment of header 18 to can 12 as indicated by welds 28.

The distal end 30 of can 12 extends beyond welds 28 to avoid exposure of any sharp and ragged surface areas, such as flash.

Stationary contact support arm 32 also formed of conventional electrically conductive material is preferably formed with a V-shaped end portion 34 to facilitate welding attachment to pin 22. It will be obvious that arm- 32 and pin 22 can be formed integrally, if it is deemed desirable. Stationary contact 40, of any good electrically conductive material, is attached to arm 32 in a suitable manner as by welding at 42.

An elongated movable contact and heater support arm 44, formed with a strengthening rib 46, is electrically connected to header 18 as by welding arcuate flange 48 of arm 44 as indicated at 50.

Heating element 52 may be formed of standard electrically resistant material and its geometry may be varied to provide the desired quantity of anticipatory heat for a given current level. One end of heater 52 is attached to the distal portion of arm 44 while the other end is attached to welding slug 54. Welding slug 54, in turn cantilever mounts thermally responsive snap acting disc element 56. Snap acting disc 56 may be formed of a conventional thermostatic composite material such as bimetal and is formed with a nondevelopable or deformed portion which is responsible for its snap action, and operates in a manner well known in the art.

Element 56, at its free end, carried an electrical contact 60 which is electrically connected thereto and is positioned for movement into and out of mating engagemen with stationary contact 40, as best seen in FIG. 2.

This is also referred to in the art as making and breaking of the contacts. Upon a predetermined increase in temperature disc 56 snaps from the solid line contacts-closed configuration seen in FIG. 2 to the opposite dashed line contacts-open configuration.

Terminals 62 and 64 are electrically attached respectively to pin 22 and can 12, as by welding. Various types of terminals can be employed to give greater flexibility to the device, such as the type shown in FIG. 5 where a pin 22a is provided with an axial bore in which lead 23 is firmly grasped by swaging.

An electrically insulating sleeve 65 formed, for example, of polymeric material, may be provided to electrically isolate the switch from its environs. To further protect fragile seal 20 electrically insulating potting material 66 may be infilled in sleeve 65 about the terminal pin 22 and seal 24.

Current flow may be traced through terminal 64, can 12, header 18, arm 44, heater 52, slug 54, disc 56, contacts 60, 40, arm 32, pin 22 to terminal 62.

The operation of switch in an exemplary circuit is as follows: The switch is electrically and thermally connected in the winding of the motor to be protected. Under normal operating conditions of the motor, the current passing through the winding also passes through the switch circuit. This current passing through the thermally responsive element 56 and the heater 52 together with the heat of the motor will not be sufficient to raise the temperature of the thermally responsive element 30 to the point where it snaps from the contacts-closed position to the opposite configuration (shown in dashed lines in FIG. 2) to break electrical contacts 40, 60 and deenergize the motor. If, however, the motor is subjected to one or more overload conditions, then heavier current will pass through heater 52 as well as thermally responsive element 56, causing the temperature to rise and element 56 to snap to the contacts-open position thus protecting the motor winding from overheating. If the motor should overheat from a loss of the refrigeration medium, this heat will be quickly transferred to the bimetallic disc due to the close thermal juxtaposition of the switch and the motor windings. A fiat surface 13 is provided on can 12 to facilitate tying of switch 10 to the winding of the motor protector as well as to enhance the thermal contact of the switch with the motor winding.

The particular configuration of movable contact support 44, heater element 52, snap acting disc 56, and stationary contact support 32 results in current flow which blows arcs created on making and breaking of contacts 40, 60 toward the closed end portion 14 of housing 12 and away from the fragile seal 24 of header 18. Also, the Z-shape configuration of arm 44, heater 52, and disc 56 permits location of contacts 40, 60 remotely from the header seal which further protects the seal from deleterious effects of the arc.

The above referred to configuration of the snap acting disc 56 and heater 52 results in a further advantage. As snap acting element 56 moves back to the dashed line position shown in FIG. 2, it moves into closer proximity to the heater element 52. The heater element then serves as a heat sink thereby maintaining the contacts in the open position for extended periods of time. This is accomplished by the generally V-shape mounting of the heater 52 and disc 56.

FIG. 4 shows a modification or second embodiment in which the distal end portion of movable contact support 44, is turned downwardly as indicated at 45. Portion 45 acts to prevent overtravel of disc 56 during snapping to the contacts open position. It should be noted that end 45 is located so that the extended are which the center of mass of contact 60 would make, as it moves from one position to another, would pass therethrough. End 45 may also be used to adjust the contact gap when the disc is in the contacts open position.

In the above embodiments the device is preferably calibrated as follows. A force 68 as seen in FIG. 4 is exerted against stationary contact support arm 32, until the desired pressure is exerted by contact 40 against mating contact and the disc snaps at the desired temperature.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above descripion or shown in the accompanying drawings shall be interpreted as illustrative and it is also intended that the appended claims shall cover all such equivalent variations.

We claim:

1. An electrical switch comprising:

(a) a tubular electrically and thermally conductive housing having a closed end and an open end;

(b) a header member hermetically attached to the open end of the housing, the header member provided with an aperture therethrough;

(c) a terminal pin extending through the aperture;

(d) glass sealing means mounting and electrically isolating the pin from the header member;

(e) a stationary contact support connected to the pin;

(f) a stationary contact mounted on the stationary contact support;

(g) an elongated movable contact support mounted on and electrically connected to the header member;

(h) a heater element having two ends, one end mounted on and electrically connected to the distal end portion of the movable contact support;

(i) a snap acting thermostatic element cantilever mounted on and electrically connected to the second end of the heater element;

(j) a movable contact mounted on the snap acting element and movable into and out of engagement with the stationary contact; and

(k) the movable contact support, heater element and snap acting element forming a generally Z-shape configuration whereby the heater acts as a heat sink to increase the off time when the snap acting element snaps to a contacts-open position and the contacts are located remotely from the glass sealing means.

2. An electrical switch comprising:

(a) a housing;

(b) an elongated movable contact support mounted in the housing;

(c) a heater element having two ends, one end electrically connected to a distal end portion of the movable contact support;

(d) a movable thermally responsive element electrically connected to the second end of the heater element;

(e) a stationary contact mounted in and electrically isolated from the housing;

(f) a movable contact mounted on the thermally responsive element, movable into and out of engage ment with the stationary contact; and

(g) the heater element and thermally responsive element forming a generally V-shape whereby the heater element acts as a heat sink for the thermally responsive element.

3. A switch according to claim 2 in which the housing is tubular with a closed end and an open end and the movable contact support forms a generally Z-shape with the heater element and thermally responsive element whereby the contacts are mounted remotely from the open end and adjacent the closed end.

4. A switch according to claim 2 in which a stop is mounted on the movable contact support to limit the travel of the thermally responsive element.

5. A switch according to claim 3 in which the tubular housing is provided with a flattened area to facilitate mounting.

6. A switch according to claim 3 in which the open end of the housing is flared and a header member is provided with a sharp edge which cooperates with the flared housing by serving as a weld projection for welding attachment thereto.

7. A switch according to claim 6 in which the free end of the open ended housing extends beyond the sharp edge of the header member.

8. A switch according to claim 3 in which an electrically insulating sleeve is placed about the switch.

9. A switch according to claim 8 in which the open end of the housing is hermetically sealed by header means; a terminal pin extends through the header means and mounts the movable contact support and stress relieving potting material is infilled in the sleeve around the terminal pin and the hermetically sealed end of the housing.

10. A switch according to claim 3 in which a header member is hermetically attached to and closes the open end of said housing, the header member is provided with 6 an aperture, a terminal pin extends therethrough and glass located in the aperture electrically isolates the pin from the header member.

11. A switch according to claim 10 in which the outer end of the pin is provided with an axial bore for reception therein of a lead wire.

References Cited UNITED STATES PATENTS 3,004,203 10/ 1961 Epstein a 337105 3,194,924 7/ 1965 Moksu et al 337-107 3,280,285 10/1966 Audette 337-107 BERNARD A. GILHEANY, Primary Examiner.

R. COHRS, Assistant Examiner.

US. Cl. X.R. 337105, 107 

